Evaluating the phytotoxicological effects of bulk and nano forms of zinc oxide on cellular respiration-related indices and differential gene expression in Hordeum vulgare L.

The increasing use of nanoparticles is driving the growth of research on their effects on living organisms. However, studies on the effects of nanoparticles on cellular respiration are still limited. The remodeling of cellular-respiration-related indices in plants induced by zinc oxide nanoparticles (nnZnO) and its bulk form (blZnO) was investigated for the first time. For this purpose, barley (Hordeum vulgare L.) seedlings were grown hydroponically for one week with the addition of test compounds at concentrations of 0, 0.3, 2, and 10 mg mL-1. The results showed that a low concentration (0.3 mg mL-1) of blZnO did not cause significant changes in the respiration efficiency, ATP content, and total reactive oxygen species (ROS) content in leaf tissues. Moreover, a dose of 0.3 mg mL-1 nnZnO increased respiration efficiency in both leaves (17 %) and roots (38 %). Under the influence of blZnO and nnZnO at medium (2 mg mL-1) and high (10 mg mL-1) concentrations, a dose-dependent decrease in respiration efficiency from 28 % to 87 % was observed. Moreover, the negative effect was greater under the influence of nnZnO. The gene transcription of the subunits of the mitochondria electron transport chain (ETC) changed mainly only under the influence of nnZnO in high concentration. Expression of the ATPase subunit gene, atp1, increased slightly (by 36 %) in leaf tissue under the influence of medium and high concentrations of test compounds, whereas in the root tissues, the atp1 mRNA level decreased significantly (1.6-2.9 times) in all treatments. A dramatic decrease (1.5-2.4 times) in ATP content was also detected in the roots. Against the background of overexpression of the AOX1d1 gene, an isoform of alternative oxidase (AOX), the total ROS content in leaves decreased (with the exception of 10 mg mL-1 nnZnO). However, in the roots, where the pressure of the stress factor is higher, there was a significant increase in ROS levels, with a maximum six-fold increase under 10 mg mL-1 nnZnO. A significant decrease in transcript levels of the pentose phosphate pathway and glycolytic enzymes was also shown in the root tissues compared to leaves. Thus, the disruption of oxidative phosphorylation leads to a decrease in ATP synthesis and an increase in ROS production; concomitantly reducing the efficiency of cellular respiration.

Effects of bulk and nano-ZnO particles on functioning of photosynthetic apparatus in barley (Hordeum vulgare L.).

The functioning of the photosynthetic apparatus in barley (Hordeum vulgare L.) after 7-days of exposure to bulk (b-ZnO) and nanosized ZnO (n-ZnO) (300, 2000, and 10,000 mg/l) has been investigated. An impact on the amount of chlorophylls, photosynthetic efficiency, as well as the zinc accumulation in chloroplasts was demonstrated. Violation of the chloroplast fine structure was revealed. These changes were generally more pronounced with n-ZnO exposure, especially at high concentrations. For instance, the chlorophyll deficiency under 10,000 mg/l b-ZnO treatment was 31% and with exposure to 10,000 mg/l n-ZnO, the chlorophyll deficiency was already 52%. The expression analysis of the photosynthetic genes revealed their different sensitivity to b-ZnO and n-ZnO exposure. The genes encoding subunits of photosystem II (PSII) and, to a slightly lesser extent, photosystem I (PSI) showed the highest suppression of transcriptional levels. The mRNA levels of the subunits of cytochrome-b6f, NADH dehydrogenase, ribulose-1,5-bisphosphate carboxylase and ATP synthase, which, in addition to linear electron flow (LEF), participate in cyclic electron flow (CEF) and autotrophic CO2 fixation, were more stable or increased under b-ZnO and n-ZnO treatments. At the same time, CEF was increased. It was assumed that under the action of b-ZnO and n-ZnO, the processes of LEF are disrupted, and CEF is activated. This allows the plant to prevent photo-oxidation and compensate for the lack of ATP for the CO2 fixation process, thereby ensuring the stability of photosynthetic function in the initial stages of stress factor exposure. The study of photosynthetic structures of crops is important from the point of view of understanding the risks of reducing the production potential and the level of food security due to the growing use of nanoparticles in agriculture.

Dependence of maize yield on hydrothermal factors in various agro-climatic zones of the Rostov region of Russia in the context of climate change.

Trends in mean monthly temperature and precipitation during the growing season and their effects on the maize yield were analyzed at the Zimovnikovsky (Zim) and Rostov (Ros) state variety plots (SVPs), located in different agro-climatic zones of the Rostov region. For these two SVPs, in the period of 1975-2019, the Mann-Kendall test showed a statistically significant increase (p < 0.05) in mean temperature (0.70 and 0.52 °C/decade) and a trend of decreased total precipitation (- 14.81 and - 10.40 mm/decade) during the maize growing season. The dependence of the maize yield on hydrothermal factors was estimated for the period of 2011-2019 using the Pearson correlation coefficient (p < 0.05). The mean temperature in September at Zim negatively (r = - 0.78), and in June at Ros positively (r = 0.77) correlated with yield, which explained, according to the value of the coefficient of determination (R2), up to 60.7% and 58.7%, respectively, of the interannual variability of the maize yield. The precipitation in July at the Zim and Ros positively correlated (r = 0.75 and r = 0.71) with yield and explained up to 55.9% and 50.6%, respectively, of the interannual variability of the maize yield. The total amount of precipitation during the growing season at Zim was the dominant factor, explaining up to 75.7% of the interannual variability of maize yield. The continuation of the observed climatic trends during the growing season could lead in the next decade to both a decrease in the maize yield by an average of 0.25 t/ha at Zim and an increase in the maize yield by an average of 0.42 t/ha at Ros.

Effects of ZnO nanoparticles and its bulk form on growth, antioxidant defense system and expression of oxidative stress related genes in Hordeum vulgare L.

A comparative analysis of physio-biochemical indices and transcriptional activity of oxidative stress genes in barley (Hordeum vulgare L.) seedlings after 7-days exposure to bulk- and nano-ZnO (300 and 2000 mg/L) was carried out. A dose-dependent reduction in the length and weight of roots and shoots, as well as a significant accumulation of Zn in plant parts, was shown. Alterations in the shape and size of organelles, cytoplasmic vacuolization, and chloroplast and mitochondrial disorganization were also revealed. These processes are particularly pronounced when H. vulgare is exposed to the higher concentrations of nano-ZnO. The study of the antioxidant defense system revealed mainly an increase in the level of reduced glutathione and the activities of superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and glutathione S-transferase (GST). The increases in activity, by 4-fold and 3-fold, was found for glutathione transferase in the roots when exposed to 2000 mg/L bulk- and nano-ZnO, respectively. The study of transcriptional activity demonstrated that in the roots under the influence of bulk- and nano-ZnO, along with Mn-SOD, Fe-SOD is highly expressed, mainly associated with the protection of chloroplasts. Analysis of the Cat 1 and Cat 2 gene expression showed that the main contribution to the increase in catalase activity in treated H. vulgare is made by the CAT-1 isozyme. Generally, in response to the impact of the studied ZnO forms, the antioxidant defense system is activated in H. vulgare, which effectively prevents the progression of oxidative stress in early stages of plant ontogenesis. Nevertheless, with constant exposure to bulk- and nano-ZnO at high concentrations, such activation leads to a depletion of the plant's energy resources, which negatively affects its growth and development. The results obtained could be useful in predicting the risks associated with the further transfer of nano-ZnO to the environment.

Toxicity of copper oxide nanoparticles on spring barley (Hordeum sativum distichum).

The rapid growth of copper oxide nanoparticles (CuO NPs) production and its abundant uses in many industries, and increasing release into an environment from both intentional and unintentional sources, create risks to spring barley (Hordeum sativum distichum), one of the most important staple food crop. Thereby, the aim of this study was to investigate the phytotoxicity of CuO NPs on H. sativum growth in hydroponic system. The CuO NPs inhibited H. sativum growth by affecting the germination rate, root and shoot lengths, maximal quantum yield of photosystem II, and transpiration rate. Structural and ultrastructural examination of H. sativum tissues using light, transmission and scanning electron microscopy showed effects on stomatal aperture and root morphology, metaxylem size and changes in cellular organelles (plastids, mitochondria), as well as in plastoglobules, starch granules, protoplasm, and membranes. The formation of electron-dense materials was noted in the intercellular space of cells of CuO NPs-treated plants. In addition, relative root length was one-third (35%) that of the control, and relative shoot length (10%) was also reduced. Further, the Cu content of roots and leaves of CuO NPs-treated plants was 5.7 and 6.4-folds higher than the control (without CuO NPs), respectively. Presented data were significant at p ≤ 0.05 compared to control. Conclusively, the results provide insights into our understanding of CuO NPs toxicity on H. sativum, and findings could be used for developing strategies for safe disposal of NPs.